1. Field of the Invention
The present invention relates to compressors, and more particularly, to a reciprocating compressor having an improved coupling part structure of a piston and a connecting rod.
2. Background of the Related Art
The compressor boosts a pressure of a working fluid by receiving a power from an electric motor or a turbine, and applying a compressive work to air, refrigerant, or other special gas. The compressor is widely used starting from home appliances, to plant industries in the fields of air conditioners or refrigerators.
Depending on methods of compression, there are positive displacement compressors, and dynamic compressors, or turbo compressors. The positive displacement compressors boost a pressure by reduction of a volume, and have reciprocating compressors, and rotary compressors.
The reciprocating compressor, compressing the working fluid by means of a piston reciprocating inside of a cylinder, is advantageous in that a high compression efficiency can be provided by using comparatively simple mechanical components.
The rotary compressor, compressing the working fluid by means of a roller revolved inside of a cylinder with an eccentricity, can provide a high compression efficiency at a speed lower than the reciprocating compressor.
FIG. 1 illustrates a typical example of the reciprocating compressor, referring to which the reciprocating compressor will be described in more detail.
Referring to FIG. 1, two pieces of cases 1 assembled together form an enclosed space, in which a frame 2 is provided. The frame 2 is supported on the cases 1 with springs 4.
There is a crank shaft 6 mounted passed through a central part of the frame 2. For this, there is a boss 3 in the central part of the frame 2 for stable support of the crank shaft 6.
The crank shaft 6 mounted thus, is rotated by the motor 5, which is provided with a stator 5a and a rotor 5b. The stator 5a is fixed to the frame 2, and the rotor 5b is fixed to the crank shaft 6. Since the rotor 5b positions inside of the stator 5a, the crank shaft 6 rotates together with the rotor 5b when power is provided to the motor 5.
Referring to FIG. 1, there is an eccentric pin 6a on top of the crank shaft 6 at an eccentric position from a rotation center of the crank shaft 6. There is a balance weight 6b on top of the crank shaft at an opposite side of the eccentric pin 6a. The balance weight 6b prevents the crank shaft 6 from shaking due to weight of the eccentric pin 6a during rotation of the crank shaft 6.
In the meantime, there is lubricating oil held on a bottom of the case 1, and the crank shaft 6 has oil passages 6c inside of the crank shaft 6. The crank shaft 6 has a pumping device 6d, such as a propeller, at a lower end. Accordingly, when the crank shaft 6 rotates, lubricating oil pumped by the pumping device moves following the oil passage 6c, and sprayed from the top of the crank shaft 6. According to this, the lubricating oil is supplied to all mechanically operative components in the case 1.
There is a cylinder 10 having a compression chamber 11 therein on top, and in one side part, of the frame 2 (see FIG. 2). There is a piston 15 coupled to the eccentric pin 6a, and provided in the compression chamber 1, which will be described in more detail with reference to FIGS. 2 and 3.
Referring to FIG. 1, the cylinder 10 is formed on top of, and as one unit with the frame 2. The piston 15 in the compression chamber 11 reciprocates within the cylinder 10 by the connecting rod 7 when the crank shaft 6 rotates.
For this, the connecting rod 7 has one end, for an example, a big end connected with the eccentric pin 6a of the crank shaft 6, and the other end, for an example, a small end 7a coupled to the piston 15.
Referring to FIGS. 2 and 3, the small end 7a of the connecting rod 7 is coupled to the piston 15 with a piston pin 15c. For this, the small end 7a of the connecting rod 7 is inserted in a piston chamber 15a, a hollow in one side of the piston 15, and the piston pin 15c passes through a pin hole 15b in the piston 15 and the small end 7a at the same time.
According to this, the connecting rod 7 can swing around the piston pin 15c within a preset angle, and there is a clearance ‘c’ between an inside surface of the small end 7a, and the outside circumferential surface of the piston pin 15c, for the lubricating oil to form a film.
In the meantime, there is a valve assembly 8 at an end of the cylinder 10 for controlling flow of the working fluid, for an example, refrigerant, introduced into the compression chamber 11, compressed, and discharged from the compression chamber 11, and there is a head assembly 9 on the valve assembly 8 for guiding flow of the working fluid.
For reference, the unexplained numeral 12 denotes a suction pipe for introducing refrigerant into the case 1, 13 denotes a suction muffler for attenuating flow noise of the refrigerant introduced through a suction pipe, and 14 denotes a discharge pipe for discharging compressed refrigerant to an outside of the compressor.
In the operation, upon application of power to the motor 5, the rotor 5b and the crank shaft 6 rotate, and the rotation of the crank shaft 6 is converted into a linear reciprocating movement of the piston 15 by the connecting rod 7 connected to the eccentric pin 5b. Therefore, the refrigerant introduced into the compressor through the suction pipe 12 is compressed by the piston 15 reciprocating in the cylinder 10, and discharged to an outside of the compressor through the discharge pipe 14.
However, the related art compressor has the following problem.
For the rotation of the small end 7a of the connecting rod 7 coupled to the piston 15 with the piston pin 15c around the piston pin 15c within a preset range of angle, supply of lubricating oil to the clearance ‘c’ is required.
However, referring to FIG. 3, in a compression stroke when the connecting rod 7 presses the piston up to a top dead center, the piston pin 15c is pushed toward the connecting rod 7, to leave almost no clearance ‘c’ and make a pressure of the lubricating oil forming a film in the clearance ‘c’ suddenly high, which causes cavitation and noise.
Moreover, as the pressure of the lubricating oil inside of the clearance ‘c’ rises, there is a force for making the lubricating oil to escape from the clearance. In this case, as shown in FIG. 3, the small end 7a of the connecting rod 7 is pushed up. According to this, periodical movement of the small end 7a of the connecting rod 7 in a length direction of the piston pin 15c is occurred, that causes noise.